This invention relates generally to the field of collapsible reusable shipping containers of a type disclosed in my prior U.S. Pat. No. 3,443,737 dated Apr. 13, 1969, and more particularly to an improved form thereof. Reference is also made to U.S. Pat. No. 4,252,266, which discloses a related invention.
Such shipping containers are primarily used for air and truck transport, where considerations of space and weight are normally of greater importance than the cost of fabrication, particularly where the container may be reused as many as one half dozen or more times before it becomes so worn that it must be discarded. However, in recent years, the cost of manufacture has increased substantially, and is currently a factor of more than nominal importance.
While conventional wood pallets or the synthetic resinous equivalent thereof have been considered an essential part of the container, which is otherwise formed of multi-ply corrugated fiberboard, such pallets are relatively heavy, and occupy a height of forty six inches which might otherwise be occupied by actual cargo. In conventional constructions, the side walls of the container are fastened to the upper or side surfaces of the pallet, and rely upon the pallet for structural rigidity. It has not heretofore been appreciated that the same side walls possess unutilized strength both in tension and compression in the plane of said side walls.
In my abovementioned copending application, Ser. No. 157,416, there is disclosed a collapsible shipping container of the class described in which the conventional pallet element of wood or synthetic resinous material has been eliminated with a corresponding saving in the cost of manufacture, occupied space, and weight. In lieu thereof, the lower edges of the side walls are glued or otherwise secured to the upper surface of a planar fiber base member, the outer edges of which extend outwardly of the plane of the outer surfaces of the side walls. The gluing of the lower edge flaps of the side walls to the upper surface thereof provides substantial additional rigidity in the planes of the walls to enable the container to function without a conventional pallet.
While this structure is suitable for many types of loads, in the case of very dense loading, as encountered with fluid or particulate materials, stresses are placed upon the side walls in planes normal to the planes of the walls which tend to cause bulging particularly adjacent the lower edges of the side walls, as well as against the lower portions of the folding doors which are not as securely entered as the remaining side wall, the lower edge flaps of which are glued to the upper surfaces of the horizontal fiber member which replaces the pallet.